The present invention pertains to semiconductor laser packages, transmitters, and receivers, and more particularly to the packaging of a plurality of optoelectronic components within TO-can package configurations.
Lasers are used for many purposes particularly in the telecommunications industry. Edge emitting lasers are the most common. They are available for all major telecommunication wavelengths and multiple types are available for various applications. Vertical cavity surface emitting lasers (VCSELs) generally offer a low-cost alternative and are capable of being fabricated in larger volumes on semiconductor wafers. These lasers, which emit light vertically from the surface of a fabricated wafer, combine the surface emission and low production cost as with light-emitting diodes (LEDs), and provide the necessary speed and power for many laser applications. VCSELs operating at wavelengths at 850 nm are often selected today as laser sources for commercial 10 Gigabit Ethernet networks and optical backplane systems.
A widely accepted package for VCSELs and edge emitting lasers is commonly known as TO-style or TO-can packages. Many conventional semiconductor laser apparatus utilize a metal or composite TO-can package for optoelectronic packaging, which includes a can and header assembly that is formed with a window or lens. The laser emissions from a laser contained within the package passes through the header or cap portion of the TO-can. The TO-can design has been used to package electronic devices since the early days of transistor technology and include characteristic features such as these windowed tops and related fiber pigtailing. The wide availability of relatively inexpensive TO-can parts and packaging services makes it a very attractive package for optoelectronic devices. Presently, relatively small TO-cans such as TO-18, TO-46 or TO-56 are used for optoelectronic packaging that accommodate data rates as high as 2.5 and 3.3 Gbps. The TO-can package however was not originally designed for relatively high Gbps speeds. High-speed optoelectronic devices have primarily relied on other more expensive laser packaging solutions such as butterfly modules.
The parasitic reactance associated with the construction of a TO-can package limited its operation for high-speed applications in the past. Speeds of up to a few gigabits per second have been achieved by implementing a “differential” drive approach well known in the art. This approach minimizes the effect of the parasitics associated with the grounding of the package. A virtual ground is established that limits current flow through the physical ground. Maintaining the balance between the differential signals is crucial however and this task gets progressively more difficult at higher speeds. Moreover, TO-can packages generally employ bond wires for connecting various optoelectronic components and posts which may further contribute to the undesirable parasitic effects often associated with these types of packages at high data rates. The current lack of adequate solutions for addressing these limitations can not meet the growing demand for high-speed digital communications services which now require optical transmission links to operate at data rates of 10 Gbps and higher.
Early transistors were packaged in metal cans. The “transistor outline package” or the “TO-can” was the first transistor package standardized by the JEDEC organization in 1960's. (JEDEC: Joint Electron Devices Engineering Council was formed in 1958.) As optoelectronic semiconductor devices such as photodetectors became available, these components were housed in TO-cans with optical windows. Although the TO-can was not originally intended to be used with high-speed modulation, it has supported increasing rates of modulation over the years. Currently, small TO-cans such as TO-46 are widely used in optoelectronic packaging at data rates as high as 2.5 and 3.3 Gbps. The wide availability of inexpensive TO-can parts and packaging services makes it a very attractive package for optoelectronic devices.